1. Field of the Invention
The present invention relates to light stabilizer packages which are capable of being blended with organic materials such as thermoplastic olefinic elastomer compounds (TPOs) to impart resistance to degradation from ultraviolet light to such materials. Compositions of these organic materials and light stabilizer packages can be molded into articles which are light stable while also being receptive for coatings of acid catalyst activated single component paint (1 pack paint) systems. In addition, the present invention relates the articles formed from these moldable light stabilized compositions.
2. Description of the Background Art
Organic materials in general, and specifically synthetic polymers, while widely utilized, have relatively poor light stability. For example, olefinic elastomer compounds tend to undergo severe deterioration when exposed to light such as sunlight or ultraviolet rays. Light stabilizers that had previously been used to increase the resistance of such olefinic elastomer compounds against light included ultraviolet light absorbers such as benzotriazole compounds and benzophenone compounds. It was later found that N-unsubstituted polyalkylpiperidine Hindered Amine Light Stabilizers (hereinafter HALS's) such as, for example, those disclosed in U.S. Pat. No. 4,241,208 of Murayama et al., provide superior protection to olefinic elastomer compounds against photo-induced degradation as compared to the ultraviolet light absorbers. Currently, photo-induced degradation of olefinic elastomer compounds such as TPOs is combatted by adding HALS to the coatings applied to an olefinic elastomeric compound otherwise formulated without any stabilizers or by including basic HALS in the olefinic elastomeric formulation.
When an HALS is added to a coating that is applied to a molded TPO article, the entire article must be coated in order to stabilize all portions of the article against ultraviolet degradation. An example of a composition of HALS that can be added to a coating that can be applied to a TPO article is described in the brochure distributed by Ciba-Geigy Corporation entitled "Tinuvin.RTM. 440 UV Light Stabilizer for Acid catalyzed Coatings" wherein a composition of 1.0%-2.0% Tinuvin.RTM. 440 by weight, based on the coating resin solid and of 2.0%-4.0% Tinuvin.RTM. 1130 by weight, based on the coating resin solids, is disclosed.
Further, it has been found that when a basic HALS compound is included as part of a TPO formulation to provide light stability to a TPO, the TPO either must remain unpainted or can only be painted with two component paint systems. It has been found that when a basic HALS compound is added to a TPO formulation to provide light stability to a TPO, the TPO cannot effectively be coated with a 1 pack paint system because such paint systems react with the compound so that the paint does not cure properly and poorly adheres to the substrate. In addition, for 1 pack paint clearcoat systems, the light stabilizing effect of the HALS compound might be neutralized, resulting in photo-degradation of the TPO. It is believed that the reason for this reaction is because basic HALS compounds react with the acidic organic pigments and curative agents of the 1 pack paint systems. Other factors affecting the paint adhesion are the affinity behavior among the components of the TPO formulation, the migration characteristics of the additives to the TPO formulation, the volatility of the additives to the TPO formulation and the thermal stability of the total system. The same problem has not been observed with two component paint systems since such systems are not acidic.
As noted above, when a TPO is coated with an HALS-containing coating, the entire molded TPO article must be coated in order to prevent ultraviolet degradation of any portion thereof. Further, current TPO stabilizer systems included as part of a TPO formulation are fully operational only when molded TPO articles do not have to be painted with 1 pack paint systems. It is often desirable for articles which are molded from such TPO formulations to be partially painted for decorative or aesthetic effects. For example, the exterior portion of automotive bumpers for certain models are made from molded TPO compositions which include conventional stabilizers, and which are pigmented to the desired color. These bumpers cannot be successfully coated with 1 pack paint systems for the reasons explained above. However, automobile designers would like to enhance the appearances of such bumpers by providing a 1 pack coating on portions thereof, while retaining the low weight and resiliency of the TPO. This cannot be accomplished with conventional TPO formulations.
Two solutions to this problem are currently known, First, it is possible to paint these articles with a two-component system, such as a polyurethane, but this results in additional process steps for coating the article as well as greater cost for the coating materials. Alternatively, it is possible to formulate the TPO without any stabilizers, but this would require coating of the entire article with a coating containing HALS, or else the uncoated areas would degrade over time when exposed to ultraviolet light.
Accordingly, a need exists for a stabilizer system that can be added to a TPO formulation to impart ultraviolet light resistance to the TPO formulations while also enabling such formulations to be unreactive toward 1-pack paint systems so that portions of the articles made from the TPOs can be painted.